This text is part of a Real Python tutorial by Isaac Rodriguez.
In Python, understanding inheritance and composition is crucial for effective object-oriented programming. Inheritance allows you to model an is a relationship, where a derived class extends the functionality of a base class. Composition, on the other hand, models a has a relationship, where a class contains objects of other classes to build complex structures. Both techniques promote code reuse, but they approach it differently.
By the end of this lesson, you’ll understand that:
- Composition and inheritance in Python model relationships between classes, enabling code reuse in different ways.
- Composition is achieved by creating classes that contain objects of other classes, allowing for flexible designs.
- Inheritance models an is a relationship, allowing derived classes to extend base class functionality.
Exploring the differences between inheritance and composition helps you choose the right approach for designing robust, maintainable Python applications. Understanding how and when to apply each concept is key to leveraging the full power of Python’s object-oriented programming capabilities.
What Are Inheritance and Composition?
Inheritance and composition are two major concepts in object-oriented programming that model the relationship between two classes. They drive the design of an application and determine how the application should evolve as new features are added or requirements change.
Both of them enable code reuse, but they do it in different ways.
What’s Inheritance?
Inheritance models what’s called an is a relationship. This means that when you have a Derived class that inherits from a Base class, you’ve created a relationship where Derived is a specialized version of Base.
Note: In an inheritance relationship:
- Classes that inherit from another are called derived classes, subclasses, or subtypes.
- Classes from which other classes are derived are called base classes or super classes.
- A derived class is said to derive, inherit, or extend a base class.
Say you have the base class Animal, and you derive from it to create a Horse class. The inheritance relationship states that Horse is an Animal. This means that Horse inherits the interface and implementation of Animal, and you can use Horse objects to replace Animal objects in the application.
What’s Composition?
Composition is a concept that models a has a relationship. It enables creating complex types by combining objects of other types. This means that a class Composite can contain an object of another class Component. This relationship means that a Composite has a Component.
Note: Classes that contain objects of other classes are usually referred to as composites, while classes that are used to create more complex types are referred to as components.
For example, your Horse class can be composed by another object of type Tail. Composition allows you to express that relationship by saying Horse has a Tail.
Composition enables you to reuse code by adding objects to other objects, as opposed to inheriting the interface and implementation of other classes. Both Horse and Dog classes can leverage the functionality of Tail through composition without deriving one class from the other.
An Overview of Inheritance in Python
You’ve already learned about inheritance in this Python for Beginners course. So, here’s a brief overview before you focus on composition and the differences between inheritance and composition.
Everything in Python is an object. Modules are objects, class definitions and functions are objects, and of course, objects created from classes are objects too.
